We report a silicon photonic circuit that can perform half-add operations using cascaded microring resonators (MRRs). Electrical pulse sequences regarded as the operands are applied to the corresponding MRRs to achieve their dynamic modulations. The final operation results are directed to the corresponding outputs in the form of light. For proof of principle, the thermo-optic modulation scheme that needs simpler fabrication processes is employed to modulate MRRs. Finally, the circuit is fabricated on an 8-in silicon-on-insulator (SOI) substrate using complementary metal-oxide-semiconductor (CMOS) technology, and the half-add operations with the speed of 10 Kb/s are demonstrated successfully.